When a luminescent pigment is applied to an opaque surface and light is shined on that surface, the luminescent pigment appears to glow. This optical property of luminescent pigments has been used in a variety of applications, including increasing the visibility of signs at night. Luminescent pigments have also been put to use in display devices, particularly toys made for children. In this application, a flexible, transparent sheet containing a luminescent pigment is overlaid on an opaque surface. When pressure is applied to the transparent sheet, it touches and adheres to the opaque surface, causing light to be reflected through the transparent sheet at the point of contact between the sheet and the opaque surface. Due to the presence of the luminescent pigment in the transparent sheet, light reflected by the opaque surface makes the sheet appear to glow where it contacts the opaque surface. The glowing image may then be erased by lifting the transparent sheet so that it no longer contacts the opaque surface. A display device of this type incorporating the use of luminescent pigments is disclosed in U.S. Pat. No. 3,761,343 to Kinberg, et al.
A similar device is disclosed in U.S. Pat. No. 4,011,665 to Port. In this device a rigid bar is used to separate a transparent, pigmented sheet from an opaque surface in order to erase a luminescent image on the transparent sheet.
More recently, a luminescent display and copying device was disclosed in U.S. Pat. No. 5,083,925 to Maruyama. This device includes a sheet of carbon paper below a semi-rigid opaque sheet. The opaque sheet is itself positioned just below a conventional transparent, pigmented sheet. When an image is traced on the transparent sheet, the pressure applied to that transparent sheet is transferred through the opaque sheet to the carbon paper. The pressure on the carbon paper then causes a duplicate of the luminescent image created on the transparent sheet to be transferred to a blank sheet of plain paper located below the carbon paper. Thus, a copy of the luminescent image traced on the transparent sheet is created on the blank sheet of paper.
Several problems have been identified with the Maruyama device and other prior art devices. The single sheet of carbon paper contemplated by Maruyama for making a copy of a displayed image, for example, only allows the creation of single-colored copies. To create a multi-colored copy with the Maruyama device, the user would have to lift the closure frame to which the carbon paper is attached and replace the sheet of carbon paper with one of another color. Replacing the carbon paper in this way is difficult and messy, especially for children. Moreover, lifting the closure frame to replace the carbon paper can cause the luminescent image on the screen to disappear. Making multi-colored copies with the Maruyama device is therefore impracticable.
A further problem with the Maruyama device is that it does not accommodate or even contemplate using different sizes of plain paper to make copies on. In addition, it is incapable of containing more than one sheet of plain paper at a time. This shortcoming in particular makes the Maruyama device more difficult for children to use, since they must open and close the closure frame of the device every time they wish to make a new drawing and a copy of that drawing.